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Polymers, Volume 7, Issue 3 (March 2015) – 10 articles , Pages 373-591

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Open AccessArticle
Keratin/Polyvinyl Alcohol Blend Films Cross-Linked by Dialdehyde Starch and Their Potential Application for Drug Release
Polymers 2015, 7(3), 580-591; https://doi.org/10.3390/polym7030580 - 23 Mar 2015
Cited by 49 | Viewed by 4104
Abstract
Feather keratin (FK) extracted from feathers represents a valuable source of biodegradable and biocompatible polymer. The aim of this study was the development and characterization of blended films based on FK and polyvinyl alcohol (PVA) cross-linked by dialdehyde starch (DAS) for a potential [...] Read more.
Feather keratin (FK) extracted from feathers represents a valuable source of biodegradable and biocompatible polymer. The aim of this study was the development and characterization of blended films based on FK and polyvinyl alcohol (PVA) cross-linked by dialdehyde starch (DAS) for a potential drug release application. The compatibility of FK/PVA was improved when cross-linked by DAS: the relative crystallinity of the PVA/FK film slightly decreased, and the enthalpy value for the melting peak decreased by about 50% for the cross-linked films. The total soluble mass of all blend films in water was below 35% at 37 °C, indicating a good stability of the films in water. The results of the Rhodamine B dye (as a model drug) release tests showed that the release rates decreased with increasing DAS content. DAS-induced cross-linking improves several important properties of the FK/PVA films, such as the compactness, the compatibility, and the stability in water. These improvements offer the potential to expand the application of FK films in the biomaterial field. Full article
(This article belongs to the Collection Polysaccharides)
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Open AccessReview
Chitosan: Gels and Interfacial Properties
Polymers 2015, 7(3), 552-579; https://doi.org/10.3390/polym7030552 - 13 Mar 2015
Cited by 124 | Viewed by 8583
Abstract
Chitosan is a unique biopolymer in the respect that it is abundant, cationic, low-toxic, non-immunogenic and biodegradable. The relative occurrence of the two monomeric building units (N-acetyl-glucosamine and d-glucosamine) is crucial to whether chitosan is predominantly an ampholyte or predominantly a [...] Read more.
Chitosan is a unique biopolymer in the respect that it is abundant, cationic, low-toxic, non-immunogenic and biodegradable. The relative occurrence of the two monomeric building units (N-acetyl-glucosamine and d-glucosamine) is crucial to whether chitosan is predominantly an ampholyte or predominantly a polyelectrolyte at acidic pH-values. The chemical composition is not only crucial to its surface activity properties, but also to whether and why chitosan can undergo a sol–gel transition. This review gives an overview of chitosan hydrogels and their biomedical applications, e.g., in tissue engineering and drug delivery, as well as the chitosan’s surface activity and its role in emulsion formation, stabilization and destabilization. Previously unpublished original data where chitosan acts as an emulsifier and flocculant are presented and discussed, showing that highly-acetylated chitosans can act both as an emulsifier and as a flocculant. Full article
(This article belongs to the Collection Polysaccharides)
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Open AccessArticle
Study on the Effect of Silanization and Improvement in the Tensile Behavior of Graphene-Chitosan-Composite
Polymers 2015, 7(3), 527-551; https://doi.org/10.3390/polym7030527 - 13 Mar 2015
Cited by 44 | Viewed by 5654
Abstract
In the present study, silane-functionalized graphene (f-graphene)-reinforced chitosan nanocomposite films exhibiting enhanced mechanical properties have been prepared by the solution casting method. These nanocomposite films were characterized by X-ray diffraction, Raman spectroscopy and thermogravimetric analysis. In order to investigate the effect of silane [...] Read more.
In the present study, silane-functionalized graphene (f-graphene)-reinforced chitosan nanocomposite films exhibiting enhanced mechanical properties have been prepared by the solution casting method. These nanocomposite films were characterized by X-ray diffraction, Raman spectroscopy and thermogravimetric analysis. In order to investigate the effect of silane functionalization, tensile tests were performed on original, oxidized and silane-functionalized graphene-reinforced chitosan nanocomposite films. Tensile results show that silane functionalization groups offer a substantial increase in the interfacial adhesion between filler and host matrix. This result is also confirmed by the surface morphology of the fracture surface in scanning electron microscope analysis. Qualitative analysis using Raman and Fourier transform infrared spectroscopy revealed the existence of Si–O–Si and Si–O–C bonds in the silanized composite. Thermal analysis of the samples shows that the material is stable up till 250 °C and maintains its thermal stability all throughout the process until it starts degrading after 510 °C. Atomic force microscopy reveals that the material is well exfoliated after the oxidation of graphene and also displays the existence of 3–6 layers of exfoliated graphene sheets. X-ray photoelectron spectroscopy studies also reveal the existence of silicon in the single state and quantify the sample to be approximately around 4% (±0.5%) of the total atomic weight. Full article
(This article belongs to the Collection Polysaccharides)
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Open AccessReview
An Overview of Mode of Action and Analytical Methods for Evaluation of Gas Phase Activities of Flame Retardants
Polymers 2015, 7(3), 504-526; https://doi.org/10.3390/polym7030504 - 10 Mar 2015
Cited by 52 | Viewed by 4481
Abstract
The latest techniques used to prove, describe and analyze the gas phase activity of a fire retardant used in polymeric materials are briefly reviewed. Classical techniques, such as thermogravimetric analysis or microscale combustion calorimetry, as well as complex and advanced analytical techniques, such [...] Read more.
The latest techniques used to prove, describe and analyze the gas phase activity of a fire retardant used in polymeric materials are briefly reviewed. Classical techniques, such as thermogravimetric analysis or microscale combustion calorimetry, as well as complex and advanced analytical techniques, such as modified microscale combustion calorimeter (MCC), molecular beam mass spectroscopy and vacuum ultra violet (VUV) photoionization spectroscopy coupled with time of flight MS (TOF-MS), are described in this review. The recent advances in analytical techniques help not only in determining the gas phase activity of the flame-retardants but also identify possible reactive species responsible for gas phase flame inhibition. The complete understanding of the decomposition pathways and the flame retardant activity of a flame retardant system is essential for the development of new eco-friendly-tailored flame retardant molecules with high flame retardant efficiency. Full article
(This article belongs to the Special Issue Advances in Flame Retardant Polymers)
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Open AccessArticle
Effects of RAFT Agent on the Selective Approach of Molecularly Imprinted Polymers
Polymers 2015, 7(3), 484-503; https://doi.org/10.3390/polym7030484 - 06 Mar 2015
Cited by 11 | Viewed by 3535
Abstract
Two types of reversible addition-fragmentation chain transfer molecularly imprinted polymers (RAFT-MIPs) were synthesized using different monomers, which were methacrylic acid functionalized β-cyclodextrin (MAA-β-CD) and 2-hydroxyethyl methacrylate functionalized β-cyclodextrin (HEMA-β-CD), via reversible addition-fragmentation chain transfer (RAFT) polymerization, and were represented as RAFT-MIP(MAA-β-CD) [...] Read more.
Two types of reversible addition-fragmentation chain transfer molecularly imprinted polymers (RAFT-MIPs) were synthesized using different monomers, which were methacrylic acid functionalized β-cyclodextrin (MAA-β-CD) and 2-hydroxyethyl methacrylate functionalized β-cyclodextrin (HEMA-β-CD), via reversible addition-fragmentation chain transfer (RAFT) polymerization, and were represented as RAFT-MIP(MAA-β-CD) and RAFT-MIP(HEMA-β-CD), respectively. Both RAFT-MIPs were systematically characterized using Fourier Transform Infrared Spectroscopy (FTIR), Field Emission Scanning Electron Microscopy (FESEM), Brunauer-Emmett-Teller (BET), and rebinding experimental study. The results were compared with MIPs synthesized via the traditional radical polymerization (TRP) process, and were represented as MIP(MAA-β-CD) and MIP(HEMA-β-CD). Morphology results show that RAFT-MIP(MAA-β-CD) has a slightly spherical feature with a sponge-like form, while RAFT-MIP(HEMA-β-CD) has a compact surface. BET results show that the surface area of RAFT-MIP(MAA-β-CD) is higher than MIP(MAA-β-CD), while the RAFT-MIP(HEMA-β-CD) surface area is lower than that of MIP(HEMA-β-CD). Rebinding experiments indicate that the RAFT agent increased the binding capacity of RAFT-MIP(MAA-β-CD), but not of RAFT-MIP(HEMA-β-CD), which proves that a RAFT agent does not always improve the recognition affinity and selective adsorption of MIPs. The usability of a RAFT agent depends on the monomer used to generate potential MIPs. Full article
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Open AccessArticle
Synthesis of Bio-Based Poly(lactic acid-co-10-hydroxy decanoate) Copolymers with High Thermal Stability and Ductility
Polymers 2015, 7(3), 468-483; https://doi.org/10.3390/polym7030468 - 05 Mar 2015
Cited by 12 | Viewed by 4594
Abstract
Novel bio-based aliphatic copolyesters, poly(lactic acid-co-10-hydroxy decanoate) (P(LA-co-HDA), PLH), were successfully synthesized from lactic acid (LA) and 10-hydroxycapric acid (HDA) by a thermal polycondensation process, in the presence of p-toluenesulfonic acid (p-TSA) and SnCl2·2H [...] Read more.
Novel bio-based aliphatic copolyesters, poly(lactic acid-co-10-hydroxy decanoate) (P(LA-co-HDA), PLH), were successfully synthesized from lactic acid (LA) and 10-hydroxycapric acid (HDA) by a thermal polycondensation process, in the presence of p-toluenesulfonic acid (p-TSA) and SnCl2·2H2O as co-catalyst. The copolymer structure was characterized by Fourier transform infrared (FTIR) and proton nuclear magnetic resonance (1H NMR). The weight average molecular weights (Mw) of PLH, from gel permeation chromatography (GPC) measurements, were controlled from 18,500 to 37,900 by changing the molar ratios of LA and HDA. Thermogravimetric analysis (TGA) results showed that PLH had excellent thermal stability, and the decomposition temperature at the maximum rate was above 280 °C. The glass transition temperature (Tg) and melting temperature (Tm) of PLH decreased continuously with increasing the HDA composition by differential scanning calorimetry (DSC) measurements. PLH showed high ductility, and the breaking elongation increased significantly by the increment of the HDA composition. Moreover, the PLH copolymer could degrade in buffer solution. The cell adhesion results showed that PLH had good biocompatibility with NIH/3T3 cells. The bio-based PLH copolymers have potential applications as thermoplastics, elastomers or impact modifiers in the biomedical, industrial and agricultural fields. Full article
(This article belongs to the Special Issue Precision Polymer Synthesis)
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Open AccessArticle
Pyrolysis Combustion Flow Calorimetry Studies on Some Reactively Modified Polymers
Polymers 2015, 7(3), 453-467; https://doi.org/10.3390/polym7030453 - 02 Mar 2015
Cited by 18 | Viewed by 4136
Abstract
As a part of our continuing work to improve the flame retardance of some chain-growth polymers, by employing a reactive route, we have synthesized several unsaturated compounds containing either phosphorus (P), or both phosphorus (P) and nitrogen (N), bearing groups in different chemical [...] Read more.
As a part of our continuing work to improve the flame retardance of some chain-growth polymers, by employing a reactive route, we have synthesized several unsaturated compounds containing either phosphorus (P), or both phosphorus (P) and nitrogen (N), bearing groups in different chemical environments. They included: diethyl(acryloyloxymethyl)phosphonate (DEAMP); diethyl(1-acryloyloxyethyl)phosphonate (DE1AEP); diethyl-2-(acryloyloxy)ethyl phosphate (DEAEP); diethyl-2-(metharyloyloxy)ethyl phosphate (DEMEP); acrylic acid-2-(diethoxyphosphorylamino)ethyl ester (ADEPAE); acrylic acid-2-[(diethoxyphosphoryl)methyl amino]ethyl ester (ADEPMAE). Acrylonitrile (AN), methyl methacrylate (MMA) and styrene (S) were free radically copolymerised with the above mentioned comonomers. The recovered polymers were subjected to routine spectroscopic and thermo-gravimetric analyses. In addition, the combustion behaviours of homopolymers as well as the copolymers containing nominal loadings of P-, or P/N-, groups were, primarily, evaluated using pyrolysis combustion flow calorimetry (PCFC). PCFC has been found to be a very useful screening technique, especially, in establishing the efficacies of the different modifying groups towards flame retarding some base polymeric materials. Values of the heat release capacity (HRC) values normalised to the P contents (wt%) can be considered as useful tool in ranking the various P-containing modifying groups in terms of their efficacies to flame-retard non-halogenated chain-growth polymers considered in the present work. Full article
(This article belongs to the Special Issue Advances in Flame Retardant Polymers)
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Open AccessArticle
Facile Synthesis of Well-Defined MDMO-PPV Containing (Tri)Block—Copolymers via Controlled Radical Polymerization and CuAAC Conjugation
Polymers 2015, 7(3), 418-452; https://doi.org/10.3390/polym7030418 - 24 Feb 2015
Cited by 13 | Viewed by 6566
Abstract
A systematic investigation into the chain transfer polymerization of the so-called radical precursor polymerization of poly(p-phenylene vinylene) (PPV) materials is presented. Polymerizations are characterized by systematic variation of chain transfer agent (CTA) concentration and reaction temperature. For the chain transfer constant, [...] Read more.
A systematic investigation into the chain transfer polymerization of the so-called radical precursor polymerization of poly(p-phenylene vinylene) (PPV) materials is presented. Polymerizations are characterized by systematic variation of chain transfer agent (CTA) concentration and reaction temperature. For the chain transfer constant, a negative activation energy of −12.8 kJ·mol−1 was deduced. Good control over molecular weight is achieved for both the sulfinyl and the dithiocarbamate route (DTC). PPVs with molecular weights ranging from thousands to ten thousands g·mol−1 were obtained. To allow for a meaningful analysis of the CTA influence, Mark–Houwink–Kuhn–Sakurada (MHKS) parameters were determined for conjugated MDMO-PPV ([2-methoxy-5-(3',7'-dimethyloctyloxy)]-1,4-phenylenevinylene) to α = 0.809 and k = 0.00002 mL·g−1. Further, high-endgroup fidelity of the CBr4-derived PPVs was proven via chain extension experiments. MDMO-PPV-Br was successfully used as macroinitiator in atom transfer radical polymerization (ATRP) with acrylates and styrene. A more polar PPV counterpart was chain extended by an acrylate in single-electron transfer living radical polymerization (SET-LRP). In a last step, copper-catalyzed azide alkyne cycloaddition (CuAAC) was used to synthesize block copolymer structures. Direct azidation followed by macromolecular conjugation showed only partial success, while the successive chain extension via ATRP followed by CuAAC afforded triblock copolymers of the poly(p-phenylene vinylene)-block-poly(tert-butyl acrylate)-block-poly(ethylene glycol) (PPV-b-PtBuA-b-PEG). Full article
(This article belongs to the Special Issue Precision Polymer Synthesis)
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Open AccessArticle
Structural and Dynamical Properties of Polyethylene/Graphene Nanocomposites through Molecular Dynamics Simulations
Polymers 2015, 7(3), 390-417; https://doi.org/10.3390/polym7030390 - 23 Feb 2015
Cited by 66 | Viewed by 5308
Abstract
Detailed atomistic (united atoms) molecular dynamics simulations of several graphene based polymer (polyethylene, PE) nanocomposite systems have been performed. Systems with graphene sheets of different sizes have been simulated at the same graphene concentration (~3%). In addition, a periodic graphene layer (“infinite sheet”) [...] Read more.
Detailed atomistic (united atoms) molecular dynamics simulations of several graphene based polymer (polyethylene, PE) nanocomposite systems have been performed. Systems with graphene sheets of different sizes have been simulated at the same graphene concentration (~3%). In addition, a periodic graphene layer (“infinite sheet”) has been studied. Results concerning structural and dynamical properties of PE chains are presented for the various systems and compared to data from a corresponding bulk system. The final properties of the material are the result of a complex effect of the graphene’s sheet size, mobility and fluctuations. A detailed investigation of density, structure and dynamics of the hybrid systems has been conducted. Particular emphasis has been given in spatial heterogeneities due to the PE/graphene interfaces, which were studied through a detailed analysis based on radial distances form the graphene’s center-of-mass. Chain segmental dynamics is found to be slower, compared to the bulk one, at the PE/graphene interface by a factor of 5 to 10. Furthermore, an analysis on the graphene sheets characteristics is presented in terms of conformational properties (i.e., wrinkling) and mobility. Full article
(This article belongs to the Special Issue Graphene-based Polymer Composites)
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Open AccessArticle
Characterization and Properties of Hydrogels Made from Neutral Soluble Chitosans
Polymers 2015, 7(3), 373-389; https://doi.org/10.3390/polym7030373 - 18 Feb 2015
Cited by 15 | Viewed by 3221
Abstract
The current paper focuses on the preparation and some characteristics of viscoelastic hydrogels, ViscoGels™, made from chitosans having a random acylation pattern. Three different chitosan batches with a high fraction of acetylation were selected based on their Mw, and the impact [...] Read more.
The current paper focuses on the preparation and some characteristics of viscoelastic hydrogels, ViscoGels™, made from chitosans having a random acylation pattern. Three different chitosan batches with a high fraction of acetylation were selected based on their Mw, and the impact of degree of cross-linking on these chitosan samples has been studied with respect to the properties of the final hydrogels. Rheological long term (12 month) stability and gelling kinetics data are presented together with results from swelling studies at different pH. Finally, an example illustrating these gels potential as drug delivery vehicles is presented and discussed. Full article
(This article belongs to the Collection Polysaccharides)
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